IIW IWS key terms

The thermal energy delivered per unit length of weld, usually calculated as arc voltage times current divided by travel speed, expressed in kJ/mm. It controls cooling rate, grain growth and hardness in the heat-affected zone.

The region of base metal adjacent to the fusion boundary that has been heated but not melted. Its microstructure and properties change according to peak temperature and cooling rate, making it a common site of cracking or softening.

A calculated index combining the carbon content with alloying elements such as manganese, chromium, molybdenum and vanadium to estimate a steel's susceptibility to hardening and cold cracking during welding.

Delayed cracking occurring below roughly 200 degrees Celsius in hardened weld metal or heat-affected zone, requiring a combination of susceptible microstructure, diffusible hydrogen and tensile restraint stress.

Hydrogen absorbed into weld metal that remains mobile at room temperature and can migrate to stressed regions, promoting delayed cracking. It is measured in millilitres per 100 grams of deposited metal.

Controlled heating of the base metal before welding to slow cooling, reduce the hardness of the heat-affected zone and allow hydrogen to escape, thereby lowering cold-cracking risk in thick or highly restrained joints.

A qualified document giving the essential, non-essential and supplementary essential variables for producing a weld, including process, consumables, joint preparation, current range, voltage, travel speed and preheat requirements.

The documented evidence that a test weld made to a draft procedure was mechanically tested and met the required acceptance criteria, forming the basis for issuing a welding procedure specification.

Assessment of an individual welder's ability to produce sound welds to a specified standard, normally by visual and destructive or radiographic examination of a test piece, with a defined range of approval.

An arc welding process in which a flux-coated consumable electrode melts to form the weld while the decomposing coating supplies shielding gas and slag protection. It is versatile and tolerant of drafts.

An arc welding process using a continuously fed bare wire electrode and an externally supplied shielding gas. Variants include short-circuiting, globular, spray and pulsed transfer modes.

An arc process using a non-consumable tungsten electrode and separately supplied filler, with inert gas shielding. It gives precise control and is widely used for root passes and thin sections.

An arc welding process in which the arc burns beneath a layer of granular flux, giving high deposition rates, deep penetration and no visible arc, suited to mechanised longitudinal and circumferential seams.

The manner in which molten metal passes from the electrode to the workpiece in GMAW, ranging from short-circuiting through globular to spray and pulsed transfer, each affecting heat input, spatter and positional capability.

Gas or gas mixture supplied to protect the molten weld pool and electrode from atmospheric oxygen and nitrogen. Argon, helium, carbon dioxide and oxygen blends are chosen for the process and material.

Deflection of the welding arc from its intended path by magnetic forces, particularly with direct current and heavy sections. It causes uneven fusion and can be reduced by repositioning the earth connection.

The percentage of a ten-minute period for which a power source can deliver its rated current without overheating. It determines the practical current available for continuous production welding.

A planar imperfection where weld metal fails to bond to the base metal or to a previous pass, typically caused by insufficient heat input, wrong travel angle or inadequate cleaning of the joint faces.

An imperfection in which the weld does not extend through the full joint thickness, often from insufficient root gap, excessive root face, low current or poor fit-up. It concentrates stress and is often detected ultrasonically.

Cavities in weld metal formed by gas trapped during solidification. Causes include damp consumables, contaminated surfaces, inadequate shielding and excessive travel speed. Acceptance depends on size, quantity and location.

Non-metallic slag trapped between weld passes or between weld metal and base metal, usually from poor interpass cleaning, incorrect electrode angle or slag that solidifies before it can float out.

Examination methods that reveal imperfections without damaging the component, including visual, penetrant, magnetic particle, ultrasonic and radiographic techniques, each with different sensitivity to surface or internal flaws.

A volumetric method sending high-frequency sound waves into the material and analysing echoes from internal reflectors. It is particularly effective for planar defects such as lack of fusion and cracks.

A volumetric examination in which X-rays or gamma rays pass through the weld and expose a detector, producing an image whose density changes reveal internal cavities and inclusions, though planar defects aligned with the beam may be missed.

The first and most basic examination of a weld, checking bead profile, undercut, spatter, fit-up, dimensions and cleanliness, usually before and after other non-destructive methods are applied.

A groove melted into the base metal along the weld toe that remains unfilled, creating a stress concentration. It is caused by excessive current, poor electrode angle or too high a travel speed.

The capacity of a material to be welded under a given fabrication regime into a joint that performs satisfactorily in service. It depends on composition, thickness, restraint and the chosen process.

Control of the moisture and hydrogen content of consumables, including baking electrodes, storing flux correctly and using sealed packaging, to keep diffusible hydrogen below the level assumed in the procedure.

Granular or coated material that protects the molten weld from the atmosphere, dissolves oxides and forms slag. Its composition and dryness strongly influence weld soundness and hydrogen content.

Internal stress locked into a welded structure by non-uniform heating, cooling and shrinkage restraint. It can cause distortion, promote cracking and reduce resistance to fatigue or stress-corrosion.

Change in shape or dimensions of a welded assembly caused by shrinkage of weld metal and adjacent heated material. It is managed by balanced sequences, jigs, correct fit-up and controlled heat input.

The resistance of a structure to free contraction of a weld. High restraint raises residual stress and the risk of cracking, and is a key factor when deciding preheat and welding sequence.

Controlled heating of a completed weldment, usually below the transformation temperature, to relieve residual stress, temper hard microstructures and allow hydrogen to escape before service.

Progressive damage from repeated or fluctuating loading, which initiates at stress concentrations such as weld toes, undercut or unfused root regions and can lead to failure well below static strength.

The first pass deposited at the bottom of a joint preparation, which establishes penetration and soundness at the root. It is often the most defect-prone pass and may need back-gouging.

Removal of metal from the reverse side of a completed root pass, by grinding, chipping or arc air, before welding from that side to ensure full penetration and eliminate root imperfections.

The planned order in which passes and joints are welded, used to balance shrinkage, limit distortion and residual stress, and control heat build-up across a fabricated assembly.

Local exhaust ventilation or on-torch extraction that captures welding fume near its source before it enters the welder's breathing zone, a primary engineering control for respiratory exposure.

Airborne particulate and gaseous by-products of welding, containing metal oxides and gases such as ozone or nitrogen oxides. Exposure is controlled by extraction, general ventilation and respiratory protection.

Last-line protection worn by the welder, including flame-retardant clothing, leather gloves, safety footwear, eye and face protection against arc radiation, and respiratory protection where fume controls are insufficient.

The hazard of current passing through the body from faulty equipment, damaged cables, damp conditions or welding in confined spaces. Prevention relies on insulation, earthing, low-voltage devices and safe working practice.

Work inside an enclosed volume with restricted access, where hazards include oxygen deficiency, toxic or flammable gas and heat. It requires assessment, atmospheric testing, a permit and a standby person.

Predicting the total cost of a welded fabrication from material, consumables, labour, equipment, energy, inspection and rework. Accurate estimates depend on deposition rate, duty cycle and joint volume.

The mass of filler metal deposited per unit time, usually in kilograms per hour. It drives labour cost and is influenced by current, wire feed speed, transfer mode and process efficiency.

The rate at which consumable wire is fed into the arc. In GMAW it largely sets the welding current, and together with travel speed it determines bead size and heat input.

The non-consumable electrode in TIG welding, often alloyed with thorium, cerium or lanthanum to improve arc starting and stability. Its tip geometry affects arc shape and penetration.

Examination of test specimens cut from a weld, such as tensile, bend, impact or hardness tests, to verify mechanical properties and soundness, typically during procedure or welder qualification.

The speed at which weld metal and heat-affected zone cool through critical temperature ranges. It governs microstructure, hardness and toughness and is controlled mainly by heat input, preheat and thickness.